/*
 * Copyright 2016 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.resolver.dns;

import io.netty.channel.ChannelFactory;
import io.netty.channel.EventLoop;
import io.netty.channel.socket.DatagramChannel;
import io.netty.resolver.AddressResolver;
import io.netty.resolver.AddressResolverGroup;
import io.netty.resolver.RoundRobinInetAddressResolver;
import io.netty.resolver.NameResolver;
import io.netty.util.internal.UnstableApi;

import java.net.InetAddress;
import java.net.InetSocketAddress;

/**
 * A {@link AddressResolverGroup} of {@link DnsNameResolver}s that supports
 * random selection of destination addresses if multiple are provided by the
 * nameserver. This is ideal for use in applications that use a pool of
 * connections, for which connecting to a single resolved address would be
 * inefficient.
 */
@UnstableApi
public class RoundRobinDnsAddressResolverGroup extends DnsAddressResolverGroup
{

    public RoundRobinDnsAddressResolverGroup(
            Class<? extends DatagramChannel> channelType,
            DnsServerAddresses nameServerAddresses)
    {
        super(channelType, nameServerAddresses);
    }

    public RoundRobinDnsAddressResolverGroup(
            ChannelFactory<? extends DatagramChannel> channelFactory,
            DnsServerAddresses nameServerAddresses)
    {
        super(channelFactory, nameServerAddresses);
    }

    /**
     * We need to override this method, not
     * {@link #newNameResolver(EventLoop, ChannelFactory, DnsServerAddresses)},
     * because we need to eliminate possible caching of
     * {@link io.netty.resolver.NameResolver#resolve} by
     * {@link InflightNameResolver} created in
     * {@link #newResolver(EventLoop, ChannelFactory, DnsServerAddresses)}.
     */
    @Override
    protected final AddressResolver<InetSocketAddress> newAddressResolver(
            EventLoop eventLoop, NameResolver<InetAddress> resolver)
            throws Exception
    {
        return new RoundRobinInetAddressResolver(eventLoop, resolver)
                .asAddressResolver();
    }
}
